Variable inductance



1956 c. E. W!LLIAMS VARIABLE INDUCTANCE Filed Sept. 16, 1952 Fig. I.

Inventor": Char-|esE. /\/i||iams, 1 WW. a:

His Attorngg.

United States Patent VARIABLE INDUCTANCE Charles E. Williams, Stanmore,England, assigncr to General Electric Company, a corporation of New YorkApplication September 16, 1952, Serial No. 3tl9,342

Claims. (Cl. 336-455) This invention relates to variable inductances ofthe type comprising a magnetic core on which is wound a main windingwhose inductance is to be varied and an auxiliary winding through whichcan be passed a variable direct current for varying the magneticsaturation of the core and thus varying the effective inductance of themain winding. Such variable inductances are usually known as directcurrent saturable core reactors or trans doctors and are used, forexample, as variable impedances in electric discharge lamp operatingcircuits for increasing or decreasing the current flowing through thelamps.

The arrangement of the main and auxiliary windings of a transductor isnecessarily such that the windings are linked magnetically, and thetransductor thus acts as a transformer so that the alternating voltageacross the main winding in operation tends to induce an alternatingvoltage across the auxiliary winding; the windings are, however, usuallyarranged so that there is substantially no resultant induction ofalternating current of fundamental frequency in the auxiliary winding,this usually being effected by forming one or both of the windings intwo parts mounted in different parts of the core, and connecting anddirecting these parts so as to produce either a cancellation of magneticflux components of fundamental frequency in the part of the coreassociated with the auxiliary windings or opposition of voltages offundamental frequency induced in different parts of the auxiliarywinding.

This arrangement of the windings does not, however, prevent theinduction into the auxiliary winding of voltages of even harmonicfrequency, with resultant flow of currents of similar frequency in theauxiliary winding which is often disadvantageous, especially indischarge lamp operating circuits.

An object of the present invention is to provide an improved form ofsuch transductor where, in operation, the flow of current of evenharmonic frequency in the auxiliary winding is substantially reduced.

According to the invention, in a variable inductance (transductor) ofthe type specified wherein the main winding and the auxiliary windingare arranged so that there is substantially no resultant induction ofalternating current of fundamental frequency in the auxiliary winding inoperation, there is provided a further magnetic core associated with theauxiliary winding but not associated with any part of the main winding,whereby the etfective impedance of the auxiliary winding with respect toalternating currents of even harmonic frequency induced therein inoperation is substantially increased. The induced voltage of evenharmonic frequency causes a current to flow in the auxiliary winding,and the magnitude of this current is effectively reduced by the increased impedance of this winding.

Preferably, the said further magnetic core is made from magneticmaterial, which, in operation, saturates slowly and then only in a verystrong magnetic field. To assist the slow saturation of the core, thecore may be provided with an air-gap or a gap of non-ferromagneticmaterial. For example, the said further magnetic core may be formed froma magnetic powder which has an effective air-gap due to the powder beingembedded in a nonferromagnetic material.

The invention will be better understood from the following descriptiontaken in connection with the accompanying drawing and its scope will bepointed out in the appended claims.

In the drawing, Fig. 1 shows a cross-sectional perspective view of adouble toroidal transductor in accordance with the invention, and Fig. 2shows a cross-sectional perspective view of another form of doubletoroidal transductor also in accordance with the invention.

In the embodiment of the invention shown in Fig. 1, the double toroidaltransductor comprises two annular magnetic cores 1, 2 each ofrectangular cross-section and formed from a stack of laminations. Eachcore 1, 2 has insulatingly wound thereon a coil of wire 3, 4respectively for forming a section of the main winding of thetransductor for the passage of alternating current in operation, thecoils being wound in opposite directions.

These cores 1, 2, and coils 3, 4 wound thereon, together with a thirdannular magnetic core 5, of rectangular crosssection, formed from astack of laminations are assembled together with their longitudinal axessubstantially collinear, the third core being placed between the twocoils 3, 4 so that the adjacent surfaces 6, 7 respectively of the coil3, and core 5 and the adjacent surfaces 8, 9 of the coil 4 and core 5are in intimate but insulating contact.

The assembly formed by the two coils 3, 4 and the third core 5 is thenprovided with a further toroidal winding 10, using the said assembly asa core, for forming the auxiliary winding for the passage of directcurrent, in operation.

In operation of this embodiment of the invention, the two sections 3, 4of the alternating current winding are so connected and directed thatsubstantially no alternating current of fundamental and odd harmonicfrequency is induced into the direct current winding 10. This may bedone by connecting them, with reverse polarity effect, in parallel as inFig. l or in series as in Fig. 2. Since, due to the presence of thestack of annular laminations S, the impedance of the direct currentwinding is greatly increased, the magnitude of alternating currents ofeven harmonic frequency induced into this winding is reduced to a muchlower level than would have been the case if the said laminations 5 hadnot been included.

The embodiment of the invention shown in Fig. 2 is structurally similarto that shown in Fig. 1 save that in this embodiment the location ofsaid third core is changed and the two cores 1, 2 together with theirwinding 3, 4 respectively, are assembled together with the adjacentsurfaces 11, 12 of the coils 3, 4 respectively in intimate insulatingcontact, the longitudinal axes of the two coils being substantiallycollinear.

In this embodiment, the assembly formed by the two coils 3, 4 isprovided around its outer circumferential surface with a third core inthe form of a winding 13 of magnetic material, for example, severallayers of metal tape wound around the circumferential surface 14 of thecoil assembly. The assembly thus formed is then provided with a furthertoroidal winding 15 for forming the auxiliary winding for the passage ofdirect current in operation.

In the embodiments shown in Figs. 1 and 2, the stacks of corelaminations on which the sections of the main Winding were wound wereformed from a grain oriented high purity 50% nickel-iron alloy and wereeach dimensioned as follows? Inches Internal diameter 3.35 Externaldiameter 4.41 Thickness 0.394

' I g 7 Inches Internal diameter; 2.6 External diameter 4.7 Thickness0.11

E; In the case of the embodiment described with reference to Fig. '2',the said winding 'of magnetic material comprised 4 layers of stripformed from Stalloy, the strip having the following dimensions:

Inches Width 2.37

Thickness 0.014 Total length 62.5

In both of these embodiments to the auxiliary Winding comprised 2680turns of 22 S. W. G. enamelled copper wire.

While I have shown particular embodiments of my invention, it will beunderstood, of course, that I do not wish to be limited thereto sincemany modifications may be made and I, therefore, contemplate bytheappended claims to cover any such modifications as fall within the truespirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is: 4

1. In combination, a two-coil winding, saturable magnetic core means forsaid winding, another winding linking said core means, the coils of saidtwo coil winding being interconnected for reverse polarity, and anadditional magnetic core means linking only said other winding.

' 2; A transductor comprising, in combinationfa' twocoil winding, aseparate closed saturable magnetic core for each coil of said winding,another winding linking both of said cores, said coils beinginterconnected for reverse polarity, and a third magnetic core linkingonly said other winding.

3. A transductor comprising, in combination, a pair of similar coaxiallyseparated magnetic ring cores each provided with a surrounding toroidalconductive winding, a third magnetic ring core coaxial with said pair ofring cores and outside each of the windings thereon, said windings beinginterconnected for reverse polarity, and a third toroidally shapedconductive winding enclosing said pair of ring cores with their windingsand said third core.

4. A transductor comprising, in combination, a pair of similar coaxiallyseparated magnetic ring cores each provided with a surrounding toroidalconductive winding, a third magnetic ring core coaxial with said pair ofring cores and between the windings thereon, and a third toroidallyshaped conductive winding enclosingsaid pair of ring cores with theirwindings and said third core.

5. A transductor comprising, in combination, a pair of similar coaxiallyseparated magnetic ring cores eachprovided with a surrounding toroidalconductive winding, a third magnetic ring core coaxial with said pair ofring cores and surrounding the windings thereon, and a third toroidallyshaped conductive winding enclosing saidpair of ring cores With theirwindings and said third core.

References Cited in the tile of this patent UNITED STATES PATENTS2,359,173 Troy Sept. 26, 1944 2,544,871 Wiegand Mar. 13, 1951 2,617,090Ogle Nov. 4, 1952 2,640,164 Giel, Jr., et al May 26, 1953 2,644,109Mulder June 30, 1953

